Field of the Invention
The present invention relates to a filter operating with acoustic harmonic waves (HW filter), having at least one resonator formed by an interdigital converter and reflectors, in which an electrical resistor is connected parallel to at least one filter component in order to protect against electrostatic discharge from contact with electrostatically charged parts.
German Patent DE 43 07 726 C states that HW filters, especially filters with fine structures, are vulnerable to electrostatic discharges, and if they contact electrostatically laden parts they can be destroyed by discharge of those parts through an interdigital converter that is contained in the filter.
In a digital converter of an HW component for protecting against electrostatic discharge from contact with electrostatically charged parts, the aforementioned German patent proposes the parallel connection of a meander-shaped electrical resistor having a resistance which is defined in such a way that the time constant, including an internal resistance and an intrinsic capacitance of the voltage source formed by an electrostatically charged part, is high as compared with the time constant including the parallel resistance and intrinsic capacitance of the interdigital converter. The parallel resistance is suitably constructed on the substrate of the filter in the form of a meander-shaped integrated resistor layer.
However, with that kind of protection provision, the problem still arises of a relatively long metal structure being needed in order to construct the protective resistor next to the component parts of the HW component.